Transmission Line Tower Research Articles

FUNDAMENTALS OF CREEP, TESTING METHODS AND DEVELOPMENT OF TEST RIG FOR THE FULL-SCALE CROSSARM: A REVIEW

Most of transmission line (TL) towers are designed and fabricated in the form of lattice using galvanized steel. The crossarm of the TL is made of Neobalanocarpus or Chengal wood. Recently, it has been reported by an electrical corporation situated in Malaysia that mechanical performance of the wooden crossarm declined below their service life of 40 years due to the extreme tropical weather in Malaysia. At present, composite crossarm made of glass fibre reinforced polymer composite were introduced as substitute in the 132 kV TL tower. However, the research findings lack of information on creep life estimation for the full-scale crossarm. Hence, a new test rig has to be developed to cater the testing operation using the uniaxial tension creep test. The primary objective of this review is to provide an overview of the creep theory and the existing creep testing methodology.

Development of Compact Overhead Power Transmission Line Tower using 8-legged Configuration

Development of Compact Overhead Power Transmission Line Tower using 8-legged Configuration

Mixed Numerical Methodology for Evaluation of Low-Frequency Electric and Magnetic Fields Near Power Facilities

This paper develops a mixed finite-element, analytical solutions, equivalent surface impedance methodology for the computation of electric and magnetic field distributions near power facilities. The proposed method enables efficient consideration of conductor sag, ground surface irregularities, proximity effects of metallic components such as transmission line towers, and transformer tank walls as well as human presence. Application examples of this methodology are given, illustrating that under a single-circuit 400 kV transmission line, the maximum electric field intensity at 1.5 m height from the ground is generated at a distance of 10 m from the line center while the maximum current density induced in a human standing on the ground is developed in the ankle; the computed values are practically half of the admissible limits of 5 kV/m and 2 mA/m2, respectively, foreseen for general public exposure by international standards.

Fragility modelling framework for transmission line towers under winds

Extreme winds may expose overhead transmission lines to loads that may result in the collapse of transmission towers leading to severe economic losses. This paper develops a modelling framework to assess the fragility of transmission towers under extreme winds such as tropical storms. To this end, the wind loading on a transmission tower is represented by a combination of three wind load components (i.e., the transverse and longitudinal tower loads as well as the wire load) expressed in terms of three key wind load-related input parameters (wind speed, wind angle of attack and horizontal span of the transmission line). The wind load-carrying capacity of towers is accordingly defined by a three-dimensional convex-curve surface with the three wind load components as the principle axes. A kriging surrogate model is established for the tower capacity surface as a function of uncertain structural parameters, based on the results from the nonlinear static analysis of the tower and Latin-hypercube sampling. Accordingly, the limit state function would suggest tower failure if the wind load effect exceeds the tower capacity defined by the surface. In this framework, the tower fragility is established by the Monte Carlo simulation. If the wind intensity, wind direction and line configuration are known, the wind load components can be evaluated. Utilizing the surrogate model, the capacity surfaces of sample towers are also obtained in terms of the simulated uncertain structural parameters simulated. Comparison between the estimated wind load components and the simulated sample surfaces yields the fragility curve. The proposed framework is demonstrated by a numerical example, as well as an application to a typhoon scenario analysis in which the failure probability of a real-world long-distance transmission line is assessed.

A Vibration-Based Structural Health Monitoring System for Transmission Line Towers

In this paper, we present a vibration-based transmission tower structural health monitoring system consisting of two parts that identifies structural changes in towers. An accelerometer group realizes vibration response acquisition at different positions and reduces the risk of data loss by data compression technology. A solar cell provides the power supply. An analyser receives the data from the acceleration sensor group and calculates the transmission tower natural frequencies, and the change in the structure is determined based on natural frequencies. Then, the data are sent to the monitoring center. Furthermore, analysis of the vibration signal and the calculation method of natural frequencies are proposed. The response and natural frequencies of vibration at different wind speeds are analysed by time-domain signal, power spectral density (PSD), root mean square (RMS) and short-time Fouier transform (STFT). The natural frequency identification of the overall structure by the stochastic subspace identification (SSI) method reveals that the number of natural frequencies that can be calculated at different wind speeds is different, but the 2nd, 3rd and 4th natural frequencies can be excited. Finally, the system was tested on a 110 kV experimental transmission line. After 18 h of experimentation, the natural frequency of the overall structure of the transmission tower was determined before and after the tower leg was lifted. The results show that before and after the tower leg is lifted, the natural frequencies of each order exhibit obvious changes, and the differences in the average values can be used as the basis for judging the structural changes of the tower.

Resonant Wireless Charging System Design for 110-kV High-Voltage Transmission Line Monitoring Equipment

A novel high-voltage operation featured wireless power transfer system for monitoring equipment charging on a 110-kV high-voltage transmission line based on magnetic resonant coupling is studied and designed in this paper. With consideration of operation environment on transmission line and electrical transmission tower, an overall scheme is proposed through installation position, coupling structure, and driving topology design. In order to improve the system's suitability in high-voltage environment, related optimization methods including constraining power flow path, improving quality factor, and coupling have been adopted. Since the coupling coils are fixed at both ends of an insulator string, a barrel-shaped high-permeability material layer is added to constrain the magnetic field distribution. Moreover, cross impacts between transmission line and the charging system are analyzed. The influence of a power frequency magnetic field on the charging system is calculated and electric distribution of the insulator string with the charging system is simulated. Analysis results indicate that cross impacts can be negligible. Experimental results verify that the transmission power can meet power supply requirements and the designed charging system can be operated stably under the high-voltage condition.

Stability Analysis of Electric Transmission Line Tower Made with Composite Material Carbon Fiber Epoxy - An Innovative Approach

Stability Analysis of Electric Transmission Line Tower Made with Composite Material Carbon Fiber Epoxy - An Innovative Approach

Numerical modeling the uplift bearing capacity of transmission line tower foundation on expansive soil

To solve the energy shortage problem, transmission lines are widely built in the middle-west of China where the expansive soil is widely distributed. The transmission tower foundation may suffer wetting and shrinking load due to weathering. To solve this problem, consolidated undrained shear tests are conducted to obtain the mechanical behavior of expansive soil with different water content. The bearing behavior of pile foundation and plate foundation under uplift force are simulated by finite element method. The bearing capacity, axial force and lateral friction of pile foundation are analyzed. The bearing capacity of plate foundation is also investigated. These obtained numerical results can provide a good reference for the design of transmission line tower foundation when it is located in an expansive soil area.

Stability design of single angle member using effective stress-strain method

Single angle members are widely used in transmission line towers due to light weight and easy installation. However, angle members may experience complex behaviors such as flexural, flexural-torsional or lateral-torsional buckling due to unsymmetrical section and eccentric loading. The current design practice is generally based on the effective length method, in which semi-empirical formulas should be used to account for the actual end conditions and member initial imperfections. In contrast, advanced beam-column elements or finite shell elements should be used when using second-order direct analysis method without the need of effective length assumption. Direct model of the failure modes (i.e. local and global failure modes) of angle members is still a challenging task. This paper firstly investigates the sensitivity of the flexural-torsional buckling of eccentrically loaded members compared to the assumed flexural buckling mode about the principal minor axis which is implemented in most of available beam-column elements. Moreover, an effective stress-strain relationship representing the typical failure modes and initial imperfections, which has been calibrated by extensive finite element analysis and experimental results, is developed for the direct analysis of steel structures made of angle sections without use of the effective length method. The proposed method is so simple that it can be incorporated into any conventional beam-column elements to implement the direct analysis of angle structures. The examples show that the proposed method is sufficiently accurate and therefore it can be employed in the practical design of angle structures.

Damage Probability Assessment of Transmission Line-Tower System Under Typhoon Disaster, Based on Model-Driven and Data-Driven Views

Under the typhoon disaster, the power grid often has serious accidents caused by falling power towers and breaking lines. It is of great significance to analyze and predict the damage probability of a transmission line-tower system for disaster prevention and reduction. However, some problems existing in current models, such as complicated calculation, few factors, and so on, affect the accuracy of the prediction. Therefore, a damage probability assessment method of a transmission line-tower system under a typhoon disaster is proposed. Firstly, considering the actual wind load and the design wind load, physical models for calculating the damage probability of the transmission line and power tower are established, respectively based on model-driven thought. Then, the damage probability of the transmission line-tower system is obtained, combining the transmission line and power tower damage probability. Secondly, in order to improve prediction accuracy, this paper analyzes the historical sample data containing multiple influencing factors, such as geographic information, meteorological information, and power grid information, and then obtains the correction coefficient based on data-driven thought. Thirdly, the comprehensive damage probability of the transmission line-tower system is calculated considering the results of model-driven and data-driven thought. Ultimately, the proposed method is verified to be effective, taking typhoon ‘Mangkhut’ in 2018 as a case study.

Experimental and numerical study of the axial stiffness of bolted joints in steel lattice transmission tower legs

Steel lattice transmission towers are constructed through the bolted assembly of various sizes of angle steel members and joint slip is inevitable; ignorance of this slip, which is the prevailing practice in transmission tower design engineering, can lead to an overestimation of the axial stiffness of bolted joints. This study investigates the impact of joint slip effects under tensile loading through a series of 30 tensile tests of 10 typical bolted joint configurations (3 specimens for each tested configuration) used in classic 500 kV lattice steel transmission line towers in China. Finite element analyses were also conducted as a complement and validation of concepts. Particular focus was placed on the load-deformation/slip curves of the tensile tests. The experimental results show that the joint slip was realized through a complicated process consisting of elastic deformation caused by the frictional load transfer and the asynchronous joint slip. Meanwhile, when subjected to an incremental axial tension, the axial stiffness of the bolted joints was highly nonlinear with regard to the elastic deformation. A simplified multi-linear strain-stress model was created using the experimental data to represent this nonlinearity in finite element analysis. The results from finite element analysis of the 30 tensile tests using this multi-linear strain-stress model show that the model can well predict the failure load level and positions of rupture of the angle members. The actual average axial stiffness of the tested bolted joints during the elastic deformation process of load transfer by bolt bearing is approximately 30% of the theoretical value. Finally, a general nodal element is proposed to describe the joint slippage effects and introduce this important factor in the structural analysis of lattice transmission towers in view of safer and more reliable design.

Influence of front time on positive switching impulse discharge characteristics of UHVDC tower gaps

The front time of switching impulses has a significant influence on long air gap discharge performance, but most testing experiments have been conducted using standard impulses. Here, we carried out experiments investigating the discharge characteristics of a ±800 kV transmission line-tower gap (5–8 m) under positive switching impulses with different front times and obtained important physical parameters, such as the time and voltage of the leader inception, the leader propagation velocity, and the 50% breakdown voltage (U50). The results show that (1) the critical wave front time increases with the air gap distance; (2) for the tested gaps, the time and voltage of the leader inception show minimum dispersion when the front time is 250 μs; (3) an approximately U-shaped curve occurs between the front time and the average velocity of the continuous leader propagation, and the velocity is the slowest with a front time of 500 μs. The results illustrated that choosing standard switching impulses (250 μs/2500 μs) to conduct a discharge test in a ±800 kV transmission line-tower gap is both suitable and effective; however, when the operation voltage further increases, the front time should be increased appropriately when conducting switching impulse tests.

Field and numerical analysis on effect of axial load on the lateral response of a pile

Purpose Piles often carry combination of axial and lateral. Currently, piles are designed separately for axial and lateral load. In the literature, few information is available on the influence of axial load on lateral behaviour of the pile. This paper aims to present the results of load deformation of a pile under pure lateral load and combined axial and lateral load. Design/methodology/approach The field load tests were carried out on four different pile diameters at two different bridge sites. Moreover, the paper addresses the numerical simulation of filed load test carried out on the pile under the combination of axial and horizontal load. Findings After field load tests and numerical simulation, it was found that the vertical load had a remarkable effect on the lateral load response of a pile. The lateral deflection of the pile was decreased about 25% under the effect of vertical load. In addition to this, the results from field and numerical simulation are quite comparable. Originality/value Typical field load tests were simulated numerically. This research adds a value in the areas of pile foundation subjected to vertical and lateral load particularly for structure such as transmission line tower and jetty.

Discharge voltage prediction of UHV AC transmission line–tower air gaps by a machine learning model

Full-scale discharge tests of transmission line–tower air gaps are costly and time-consuming, and they cannot exhaustively simulate all the gap configurations in practical engineering. In this paper, a machine learning model established by support vector machine is introduced to predict the switching impulse discharge voltages of the ultra-high-voltage (UHV) AC transmission line–tower air gaps. The three-dimensional finite element models of a UHV cup-type tower and a UHV compact transmission line were established for electric field calculation, and some features were extracted from the hypothetic discharge channel and the shortest path between the bundled conductor and the tower. These features under a given voltage were normalised and input to the SVM model, while the output is two binary values, respectively, representing gap withstanding or breakdown. Trained by experimental data of one type of the UHV transmission line–tower gaps, the SVM model is able to predict the discharge voltages of another gap type. The mean absolute percentage errors of the two engineering gap types, under different gap distances, are 8.31 and 4.86%, respectively, which are acceptable for engineering applications. The results provide a possible way to obtain the discharge voltages of complicated engineering gaps by mathematical calculations.

Characteristics of the Flexible Graphite Grounding Material and its Engineering Application

In order to meet the requirements of corrosion resistance of the grounding material and thermal stability of the grounding material of the transmission line towers, under the condition of power frequency current and high-frequency lightning current scattering into the ground in the case of short-circuit fault and lightning strikes, a kind of high-current capability flexible graphite grounding material was developed. The corrosion resistance of the flexible graphite grounding material and the steel type grounding material was compared by the soil simulation solution corrosion tests. The contact performance with different soils of the two materials was analyzed by the actual contact resistance measurement test. The thermal stability and the impulse current effective length of this grounding material were studied by means of simulation calculation. The results show that the high-current capability flexible graphite grounding material has a strong anticorrosion characteristic, whose reliable service life can exceed 30 years. Compared to the round steel grounding material, the contact resistance with the soil can be reduced by approximately 30%, and the impulse current effective length can be increased by about 30%.

Low Delay Technology Research of Transmission Line Tower Monitoring Network Integrating WSN and RFID

The tower is a key component of the transmission line system and its stability and reliability is the guarantee for the safety of entire transmission line system. This paper proposes a transmission tower monitoring network integrating wireless sensor network (WSN) and radio frequency identification (RFID). Compared to current designs, the proposed monitoring network shows the advantages of low cost, fast fault locating, tracking and management of grid equipment, and long-time monitoring. Low delay design is critical for the proposed monitoring network. In order to achieve balance between transmission delay and network cost, this paper establishes the transmission delay model for sink node optimization. For the redundant data of RFID, this paper presents a novel data cleaning scheme specially for the transmission tower monitoring, which can effectively reduce the redundant data at the reader end. The simulation results show that the optimal group number is 10 according to the proposed delay model.

巨厚砂砾岩地层条件下高压线塔压煤开采与变形控制

巨厚砂砾岩地层条件下高压线塔压煤开采与变形控制

Small-diameter vertical shafts constructed in the shallow space of steep mountainous areas

Japan is a mountainous country comprising several islands, in which mountains occupy 70% of the entire land. Therefore, numerous transmission line towers have been constructed in the shallow space of steep mountainous areas. In such construction, monorails and/or cableways are generally used to transport materials and equipment to the construction site instead of using a construction road, as the former method is more economically viable. However, with this method, drill rigs or vertical shaft sinking machines cannot be transported to the site. Four small-diameter vertical shafts of 2.5 or 3.0 m as the foundation for high-voltage transmission line towers in mountainous areas are traditionally constructed manually in Japan. Over the past two decades, however, dangerous and poor environmental conditions for workers regarding the manual construction of these small-diameter vertical shafts have become a major problem. Meanwhile, owing to the poor environmental conditions of small-diameter vertical shafts to be constructed in the shallow space of steep mountainous areas, a decrease has occurred in the number of young workers entering these projects. Namely, the construction of transmission line towers with using the manually traditional small-diameter vertical shafts is becoming difficult in Japan from abovementioned problems. Hence development of a new technology to solve the problems is necessary for Japan’s economic growth. With this knowledge, the authors have developed a new small-diameter vertical shaft construction system, in which workers do not have to enter the vertical shaft during construction, as machines are used instead. The applicability of the proposed system was confirmed by means of the construction of three actual vertical shafts at two construction sites, as well as in factory and field tests. The applicability and details of the final proposed system are summarized in this paper.

Modeling of Positive Switching Impulse Discharge of UHV Transmission Line Air Gaps

Positive switching impulse discharge characteristics are an important basis for the external insulation design of transmission line towers. At present, the characteristics are obtained mainly by real tower discharge tests. Since the existing research on the discharge model is not perfect, test designs are not reasonable, which results in high costs. The influence of line height and tower width on the discharge characteristics of Ultra High Voltage (UHV) transmission lines air gaps is studied in this paper. The results show that the line height had little influence on the breakdown voltage of air gaps in UHV transmission lines. A tower-width discharge model was obtained by fitting the breakdown voltage of air gaps with different gap lengths and tower widths. By analyzing the gap characteristic factors of different transmission lines, a discharge model of different tower air gaps in UHV transmission lines was presented. The breakdown voltage calculated by the models was in good agreement with the test results, and the errors were not more than 5%.

A Method for Settlement Detection of the Transmission Line Tower under Wind Force.

In view of the settlement problem of transmission tower foundation, the vibration characteristics of transmission towers under wind force are measured experimentally. In this paper, the 110 kV cat head transmission tower of Xi’an Polytechnic University is measured and analyzed. Firstly, the acceleration sensor and meteorological sensor are installed on the tower to collect the vibration response and environment parameters of the tower in real time. Then, an experiment platform is built to simulate the tower settlement, and the vibration response of the tower after settlement is measured in time. Finally, the low-order modal frequencies of the transmission tower before and after settlement under wind force load are extracted by stochastic subspace identification (SSI), and the relationship between modal frequencies of different modes is analyzed via temperature correction. By comparison and analysis, it is obvious that the X-direction modal frequencies before and after settlement under natural wind load are changed, and the change rate increases with the increase of settlement displacement, which can be used as effective evidence for judging the settlement of transmission tower foundation.